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Chng 2 : NG DNG QU TRNH TRCH LY TRONG CNG NGH LC DUNguyn tc trch ly : Trch ly lng-lng l mt k thut phn tch da vo ha tan khc nhau (hay cn gi l s ha tan c chn lc) ca cc cu t trong nguyn liu lng ng nht vo trong mt dung mi thch hp. Nguyn liu l mt cht lng cha cc cu t cn tch. Dung mi mi l mt cht lng th hai c tc dng ko cc cu t cn tch m chng l cc cu t d ha tan vo dung mi mi nht. Nh vy trong nguyn liu ch cn li cc cu t khng th ha tan vo trong dung mi mi. Sau qu trnh trch ly, h tn ti hai pha khng tan ln. Vic phn tch hai pha c thc hin bi qu trnh gn lng. Tip theo l qu trnh tch dung mi ra khi cc pha cha n hay cn gi l qu trnh hon nguyn dung mi. Mt qu trnh trch ly bng dung mi thng i hi hai giai on chnh b tr ln nhau: giai on trch ly ni ring v giai on hon nguyn hoc ti sinh dung mi thng bng qu trnh chng ct. Cc trng hp phi s dng qu trnh trch ly: Thng thng chng ta phi s dng n qu trnh trch ly khi qu trnh chng ct khng m bo c v mt k thut: - Trng hp cc dung dch ng ph - Trng hp cc dung dch c nhit si rt gn nhau. - Mt khc do mi lin h cht ch gia ha tan v bn cht ha hc, trch ly bng dung mi c bit p ng tt i vi trng hp phn tch cc cu t theo cc h ha hc v ha tan ca cc h khc nhau l khc nhau (V d kh aromatic sn xut du nhn, sn xut nhin liu; kh asphalt sn xut du DAO). Cc phng thc trch ly: Qu trnh trch ly c th c p dng theo nhiu phng thc khc nhau: - Trch ly mt giai on, ging nh qu trnh ho hi trong chng ct v ch cho php phn tch s b, n gin, tinh khit ca cc sn phm khng cao. - Trch ly cho dng cng nh trch ly ngc dng n gin thng c quan tm hn do tit kim c dung mi nhiu hn, v c th cho pha rafinat c cc ch tiu k thut yu cu nhng c hiu sut gii hn. - Qu trnh trch ly ngc dng c hi lu, ngoi hoc ni, t ti c cc tinh khit v hiu sut mong mun i vi c hai pha rafinat v extrait. Cc ng dng trch ly trong cng nghip du kh: Trong lnh vc du m, qu trnh trch ly c p dng t lu v mt mc rt ln. Chng ta s tm hiu trong chng ny 3 ng dng quan trng ca k thut trch ly, l: Qu trnh trch ly cc hp cht thm tn ti trong du c s c tnh nhn nhm iu ch cc loi du nhn Qu trnh kh asphalt ca phn cn chng ct chn khng, thu hi trit cc loi hydrocarbon (gi l du DAO) m chng khng bay hi c trong thp chng ct chn khng (do chng c nhit si cao hn du DSV cht t). (tip du DAO nu dng ch bin du nhn th cng s phi tri qua cng on trch ly cc hp cht thm nu trn). Qu trnh trch ly cc hp cht thm BTX (Benzen, Toluen, Xylen) trong cc loi nhin liu nh trch ly Aromatic t xng, kerosen m bo cc quy nh hin hnh v trong tng lai ca nhin liu v cht t.

342.1. TRCH LY KH AROMATIC T DU C TNH NHN SN XUT DU GC Du c s l cc loi du nhn c tnh nhn c dng lm nguyn liu sn xut du gc. Cc loi du c s ny c th l: - Phn ct distilat ca qu trnh chng ct chn khng, - Du trch t cn chng ct chn khng (du DAO-Des-Aphalt-Oil) l du c kh asphalt bng trch ly vi dung mi C3, C4, C5. Du gc l cc loi sn phm du nhn ca nh my lc du qua cc qu trnh ch bin v c y cc tnh cht nht. Du nhn thng phm l cc loi sn phm du nhn ca nh my phi trn du nhn. Chng c phi trn t cc loi du gc v ph gia theo nhu cu th trng, nhm p ng mt s tiu chun thit yu no ca ng c. Cc h hydrocarbon cu thnh cc loi du c s l: Cc hp cht parafin (n-parafin c mch thng), Cc hp cht parafin mch nhnh v parafin c 1 vng naphten (i-parafin v naphten 1 vng) l cc loi hydrocarbon cn cho du thng phm, Cc hp cht polynaphten (naphten a vng), Cc hp cht aromatic. Mi lin h gia cc tnh cht dng lm du gc v cu trc ca cc hydrocarbon c trong cc phn on du c s c nu trong Tableau 7.1. Mt c tnh c bn rt quan trng ca du nht l tnh n nh t b thay i ca nht khi nhit thay i. o c tnh ny, ngi ta s dng ch s nht VI, l mt thang o quy c c trng cho s thay i nht ng hc ca mt phn on du m theo nhit . Ch s nht VI cng cao, s thay i nht theo nhit cng nh, du nhn lm vic cng tt. Ch s nht VI ca cc h hydrocarbon cu thnh cc phn on du c s c dng cho qu trnh sn xut cc loi du gc nh cc qu trnh trch ly thng thng bng dung mi l: Hydrocarbon Parafin Rafinat (dung dch lc tch aromatic, naphten) Du kh parafin Phn ct Distilat Du naphten Extrait (dung dch trch cha ch yu aromatic) VI 140-180 105-120 95-105 75-95 40-65 naphten>parafin * Cn trong cng mt h ha hc, ha tan gim khi khi lng phn t ca hydrocarbon tng ln. so snh hiu qu ca cc dung mi khc nhau, ta t chng trn gin : chn lc-kh nng ha tan, Hnh 7.30, cho h 3 cu t dung mi-benzen-hexan 25oC. Trn honh , kh nng ha tan ca dung mi c din t bng h s phn b ca benzen ban u, phn %V. Trn tung , chn lc c din t bng t l h s phn b ca benzen v hexan. Ta thy c s phn tn kh rng ca cc im, vi khuynh hng r nt tun theo quy lut nghch bin gia chn lc v kh nng ha tan. Hai dung mi c s hi ha ca 2 tnh cht l DMSO v sulfolan. Hoc mt hn hp ca hai dung mi, v d NMP v EG cng c cc tnh cht trung gian ca cc cu t ny v chng nm trn ng cho ca 2 tnh cht. Cc mi tn c trn gin ch ra rng hai tiu chun trn ca dung mi c th b thay i: Hoc bi s gia thm nc: s thm nc vo dung mi s lm gim kh nng ha tan ca dung mi v lm tng chn lc ca dung mi, Hoc bi s thay i nhit : tng nhit s ci thin kh nng ha tan ca dung

50mi nhng li lm gim tnh chn lc ca n. Trong qu trnh trch ly, nhit v hm lng nc trong dung mi l hai thng s c nh hng quyt nh i vi giai on trch ly ni ring v cng c nh hng quan trng i vi cc cng on h ngun (hon nguyn). V vy chng cn c ti u ha cho mi qu trnh. Cc iu kin vn hnh ca cc loi dung mi chnh trong thp trch ly c gii thiu trong Bng 7.27. 2.3.3.2. Cc tnh cht vt l khc Theo nh cc tnh cht vt l chnh c nu trong Bng 7.26, ta c th nhn thy ni chung cc dung mi u cn cc tnh cht sau: 1. Nhit kt tinh kh thp trong qu trnh bo qun chng khng b kt tinh. i vi cc dung mi nh sulfolan, DMSO v NFM c nhit kt tinh cao, i hi phi c cc ng ng hi trong cc thng cha lu tr. 2. Nhit si cao hn r rt nhit si ca xylen (140oC), l cht thng t bay hi nht trong cc hp cht aromatic c trch ly. Nh vy, qu trnh ti sinh dung mi t phn trch c thc hin bng phng php chng ct t nhin v do rt tit kim. 3. T trng gn hoc cao hn 1,1, iu ny bo m s khc bit v t trng vi cc hydrocarbon ca nguyn liu (khi lng ring 20oC khong 0,660-0,880 g/cm3), to iu kin tt cho s i lu cc dng trong thp trch ly v qu trnh lng phn ring cc pha. 4. nht c th l cao nhit thng, c bit i vi cc dung mi glycol (61.9 mPa.s/20oC), tuy nhin lun lun nh hn 2,5 mPa.s nhit s dng trong thp trch ly v do nht ny to iu kin cho qu trnh ng hc truyn khi din ra nhanh chng. 2.3.4. S tng qut ca qu trnh trch ly Qu trnh trch ly cc hp cht aromatic BTX cng nghip lun l qu trnh lin tc. N bao gm 7 cng on tiu biu nht c m t trn Hnh 7.31. (Tuy nhin ty tng qu trnh, s lng cc cng on c th thay i). a. Trch ly thc th b. Lm sch cho cc hp cht aromatic c. Ti sinh dung mi hay phn tch BTX/dung mi d. Ra phn lc e. Tch dung mi khi nc ra f. Lm sch dung mi g. Phn on hn hp BTX thnh cc cu t tinh khit 2.3.4.1. Cng on trch ly thc th C chc nng nng cao hiu sut tch cc hp cht aromatic ra khi nguyn liu, ngha l cung cp pha lc gn nh khng c aromatic. l qu trnh trch ly ngc dng n gin ca nguyn liu v dung mi. Phn pha trch th thu c c th cha c loi b ht cc tp cht parafin v naphten v cn phi tri qua qu trnh lm sch b sung. 2.3.4.2. Cng on lm sch cho cc hp cht aromatic C nhim v lm cho cc hp cht aromatic t c cc ch tiu k thut cui cng v tinh khit cao ca chng v hm lng cc tp cht khng phi l aromatic l thp nht. N c thc hin hoc bi qu trnh trch ly li (rextraction) hoc bi chng ct trch ly cho pha trch th.

512.3.4.3. Cng on ti sinh dung mi Hay l lm tinh khit hp cht aromatic l cng on tch dung mi ra khi cc hp cht aromatic. N bao gm mt qu trnh chng ct n gin hay qu trnh stripping bng hi nc Pa. i lc p sut chn khng khi m n nh nhit ca dung mi i hi. y l 1 cng on quan trng v khi dung mi ha tan c chn lc aromatic d dng bao nhiu th khi tch dung mi ra khi aromatic li s kh khn by nhiu. 2.3.4.4. Cng on ra phn lc th Ca qu trnh trch ly bng nc cng l cn thit, tch dung mi b cun theo pha lc, do ha tan ca dung mi vo trong cc hp cht parafin v naphten l rt nh nhng khng phi bng khng. Nc l 1 dung mi mi s ha tan trit dung mi b cun theo, s cho ta pha lc tinh khit cha cc hp cht parafin v naphten. Tuy nhin cng on ny d thc hin hn cng on trn nhiu. 2.3.4.5. Cng on tch dung mi khi nc ra Bng phng php chng ct. Dung mi thu hi s c tun hon tr li cng on trch ly. 2.3.4.6. Cng on lm sch dung mi Trong ton b cc cng on ca qu trnh trch ly, cc sn phm nng c th c hnh thnh cc cng on khc nhau (do polymer ha cc hp cht cha bo ha, phn hy dung mi hay cc phn ng ha hc khc khng mong mun), v vy hu ht cc qu trnh trch ly cc hp cht thm cn c mt cng on nh lm sch dung mi khi cc sn phm nng. Thng thng mt cng on chng ct chn khng x l lin tc hoc gin on ch khong 1% dung mi trong qu trnh tun hon. 2.3.4.7. Cng on phn on hn hp BTX thnh cc cu t tinh khit Cui cng, hn hp cc hp cht BTX tinh khit phi c phn on thnh cc cu t ring bit l: benzen, toluen v xylen. Qu trnh phn on ny khng c kh khn no c bit v c thc hin bi hai qu trnh chng ct thng thng (c th l 3 nu c nhim nc trong xylen). 2.3.5. Cc qu trnh trch ly hp cht thm trong cng nghip lc du Ta c th phn loi cc qu trnh cng nghip thnh hai nhm, ty theo chng hot ng vi mt dng dung mi duy nht (l dung mi tinh khit hoc dung mi hn hp ng nht ca vi dung mi), hay vi hai dng dung mi khng trn ln nhau gia chng. Phng php 1 dung mi c ng dng trong trng hp: - Dung mi c n nh nhit cao nn khng b phn hy trong qu trnh hon nguyn bng chng ct trch ly. - chn lc ca dung mi sulfolan cao nn ch cn 1 thp trch ly, dung mi cng ko ht aromatic ra khi pha lc (parafin-naphten), - Vic tch dung mi sulfolan ra khi pha lc rt d dng nh nc ha tan tt vi dung mi m khng ha tan vi parafin-naphten. Phng php 2 dung mi c ng dng trong trng hp:

52- Dung mi DMSO c n nh nhit thp, d b phn hy trong qu trnh hon nguyn bng chng ct trch ly (hon nguyn cng Pck) - chn lc ca dung mi DMSO thp hn, n c th ha tan c parafin-naphten nn phi c thm dung mi th 2: C4 C4 ko ht parafin-naphten ra khi pha trch (aromatic-S), - Vic tch dung mi DMSO ra khi pha lc rt d dng nh nc ha tan tt vi dung mi m khng ha tan vi parafin-naphten-aromatic v C4, chn lc ca 2 loi dung mi gim dn theo trt t sau: - C4 (ha tan tt) parafin-naphten>aromatic>DMSO v nc - DMSO>nc>aromatic>C4. 2.3.5.1. Cc qu trnh ch s dng mt dung mi, Qu trnh Shell/UOP Nm 1961, cng ty Hong gia H Lan Shell cng tc vi hng UOP M pht minh ra 1 qu trnh ch s dng mt dung mi sulfolan. So snh vi dung mi glycol, dung mi sulfolan c nng sut ln hn i vi cc hp cht aromatic, nhit si cao hn, n nh nhit tt nht v nhy km hn i vi s oxy ha. S qu trnh Shell/UOP c trnh by trong Hnh 7.32.

Cc qu trnh s dng mt dung mi duy nht mt cch tng qut bao gm 4 cng on chnh sau: 1. Trch ly cc hp cht aromatic bng dung mi sulfolan, 2. Tch nc v parafin-naphten ra khi phn trch bng chng ct trch ly, 3. Ti sinh dung mi cho phn trch bng chng ct thng thng, 4. Ti sinh dung mi cho phn lc bng vic dng nc ra ko dung mi ra.Nguyn liu c nhp vo mc thp ca thp trch ly, thp ny cng nhn dung mi sulfolan c km theo khong 1% nc nh thp, v y cc hydrocarbon c tun hon li. Thit b trch ly l thit b tip xc bng a quay RDC, hay l mt thp mm xuyn l tng ng vi khong chc bc l thuyt. N hot ng nhit khong 100oC, di p sut t 2-4 bar. T l dung mi c iu chnh sao cho tha mn vi cc tiu chun k thut v hiu sut thu aromatic v thng nm trong khong 3/1 dn 5/1 theo khi lng. Phn trch th c t thp trch ly c chuyn v nh thp chng ct trch ly c khong ba chc mm, hot ng p sut kh quyn vi t s un si tun hon ph hp cho cc hp cht aromatic y thp t c cc ch tiu k thut v hm lng cc hp cht khng aromatic. Hi nh bao gm cc hp cht khng aromatic, mt phn cc hp cht aromatic nh nht v nc b li cun theo do ng ph (c cng nhit si) vi cc hydrocarbon. Sau khi ngng t, pha hydrocarbon c lng v chuyn tr li v thp trch ly. Phn trch c lm sch ht cc cht khng phi aromatic (ch cn Ar v dung mi) c chuyn v thp bc hi cc hp cht aromatic (cng c khong ba chc mm), n c sc hi nc chn thp. Thp hot ng p sut thp (300-400mmHg) nhit y m bo n nh nhit ca dung mi, khong 180oC. Qu trnh iu khin thp c thc hin sao cho nh thu c hp cht aromatic c cc tiu chun k thut thch hp, v y dung mi ti sinh c tun hon v li thp trch ly. Nc thu hi thit b ngng t nh thp bc hi s qua cng on ra phn lc th ko ht dung mi sulfolan ra khi phn lc, sau c x l sao cho tch loi cc vt hp cht hydrocarbon khng aromatic b ha tan v c tun hon tr li trong thp bc hi. 2.3.5.2. Cc qu trnh s dng 2 dung mi

Cc qu trnh s dng hai dung mi, mt cch tng qut bao gm 5 cng on

53 chnh sau: 1. Trch ly (ln 1) cc hp cht aromatic , dng 2 dung mi ng thi (DMSO v C4): li dng tnh chn lc ca DMSO-aromatic v ca C4-naphten v parafin m tch c aromatic ra khi naphten v parafin 2. Trch ly li (ln 2), ch dng 1 dung mi C4: li dng tnh chn lc ca C4aromatic m tch c aromatic ra khi DMSO (thu c phn ln DMSO tinh khit) 3. Tch DMSO b ko theo cc phn lc ra nh ca 2 thp trch ly: li dng tnh chn lc ca nc-DMSO m tch c DMSO ra khi cc phn lc . 4. Tch hn hp nc-DMSO bng chng ct chn khng nhm thu hi trit DMSO (0,3 bar do DMSO d b phn hy v nhit) 5. Thu hi dung mi C4 t 2 phn lc ra khi thp ra bng 2 thp chng ct p sut cao: nh cc thp thu c C4 cho tun hon tr li, cn y cc thp ta thu c cc dung dch trch v lc tinh khit. Cc qu trnh s dng 2 dung mi khc bit vi cc qu trnh trn do cc giai on lm sch cc hp cht thm v ti sinh dung mi khng c thc hin bng chng ct trch ly v stripping m bng trch ly li vi mt dung mi ph. Dung mi ph phi t b trn ln vi dung mi chnh v d dng phn tch c vi cc hp cht hydrocarbon ca nguyn liu bng phng php chng ct.Cc qu trnh khc nhau c ngh, ni bt nht l vi cc dung mi tetraethylenglycol (Union Carbide), NFM (Snam Progetti), DMSO (IFP) c s dng nh dung mi trch ly v mt parafin c th hoc d bay hi hn hoc t bay hi hn cc hp cht hydrocarbon ca nguyn liu, c s dng nh dung mi trch ly li. Qu trnh DMSO-Butan, s cng ngh c trnh by trong Hnh 7.33, c pht trin bi IFP t u nhng nm 1960 v c cng nghip ha vo nm 1967. Nguyn liu c nhp vo trong thp trch ly khu vc trung gian. DMSO, c gia thm 4-6 % nc c a vo nh v Butan c a vo y thp. Qu trnh trch ly c thc hin nhit trung bnh khong 30oC v p sut 4-6 bar tuyt i nhm gi cho butan th lng. T l dung mi (DMSO/nguyn liu) c khng ch sao cho bo m c hiu sut thu aromatic ty theo thnh phn nguyn liu. Thng t l ny trong khong 3/1 n 6/1. T l Butan/nguyn liu c iu chnh ty theo cc ch tiu k thut tinh khit ca cc hp cht aromatic; t l ny thng khong 0,15/1. Phn lc th n t thit b trch ly c ra bng nc tch loi DMSO ha tan trong , sau c chng ct phn tch butan, butan c tun hon. Phn trch c a n thit b trch ly li cho tip xc ngc dng vi butan cng mt iu kin p sut v nhit nh trong thp trch ly. T l lu lng butan/trch c xc nh sao cho trch ly li c hon ton cc hp cht aromatic v trung bnh bng 0,31/1 theo khi lng. DMSO c ti sinh nh vy c cho tun hon trc tip v thp trch ly. Butan, c mang theo aromatic c ra bng nc loi DMSO bo ha c trong ri c chng ct v c tun hon v thp trch ly li. Nc ra cc hydrocarbon c cha DMSO c chng ct chn khng (200 mmHg) v c tun hon v thit b ra bng nc, nm nh cc thp trch ly. DMSO c thu hi v c ti nhp vo trong dng dung mi. Hiu qu ca s ny l dng DMSO m khng s c nguy c phn hy n. Mt thun li khc ca s ny l n c kh nng trch ly cc hp cht aromatic ca mt phn on rng, do vic phn tch aromatic/dung mi bng chng ct khng cn l vn na. Tuy nhin cn lu rng phn on cng rng th lu lng dung mi trch ly v trch ly li cng ng k i vi mt n v aromatic c trch ly. V vy c mt gii hn kinh t v x

54l cc phn on rng v nu vt qu gii hn ca phn on rng cho php th khng th p dng mang tnh cng nghip i vi trch ly cc hp cht BTX. 2.3.5.3. Cc qu trnh cng ngh in hnh a. Qu trnh Udex Qu trnh Udex c pht trin kt hp bi cc hng UOP v Dow Chemical Co., bng dung mi c c s DEG v c p dng t nm 1952. Trrong khong chc nm, n l qu trnh duy nht sn xut aromatic c ngun gc t du m vi tinh khit ln hn 99,8% v hiu sut trung bnh d 95%. Ngy nay n khng cn c quan tm nh l mt qu trnh c tnh cnh tranh na. DEG trong thc t cho nng sut aromatic tng i thp, dn n s dng cc t l dung mi ln trong qu trnh trch ly, t 6 -20, ty theo nguyn liu. Cc dung mi hiu nng cao hn thay th n. b. Qu trnh Arosolvan ca Lurgi Qu trnh ny thc hin vi dung mi c s l NMP. Trong th h u tin c cng nghip ha vo nm 1962, NMP c cng thm nc (12-14 %) ti u ha hiu qa trch ly ca n. Sau , xut hin mt dung mi hn hp NMP-glycol dn n mt qu trnh tit kim hn v nng lng, do n trnh c s ha hi nc d cng vi cc hydrocarbon trong giai on lm sch phn trch bng chng ct trch ly. T l ca glycol ph thuc vo hm lng aromatic ca nguyn liu v thng nm trong bin 40-50%. Mt c im ca qu trnh l thit b trch ly Lurgi, c thit k trn nguyn l chng cht cc thit b khuy trn-lng v c thun li l d dng c ngoi suy cho n ng knh thp khong 8m. Cc tnh cht tan ca NMP dn n vic tin hnh qu trnh trch ly nhit gn vi mi trng, khong 50oC. c. Qu trnh Tetra ca Union Carbide Qu trnh ny ly tn gi ca dung mi m n s dng: l dung mi tetraethylen glycol cng vi 4% nc. N c bit n vo nm 1968. S thay th DEG bng TETRA c kh nng ha tan ln hn cho php chia hai t l dung mi v nh vy lm tng ln 80% nng sut x l. Vi cc thit b mi, Union Carbide a ra cc cu trc bn trong c bit ca thp. l cc mm xuyn l c nhiu ng chy chuyn kiu MU (Multiple Upcomer) i vi thp trch ly v chng cho php cc lu lng ln hn cc mm thng thng, v cc mm c ng chy chuyn kiu MD (Multiple Downcomer) i vi cc thp stripping cc hp cht khng aromatic. Thp ny trong thc t cn phi c cc cu trc bn trong t l vi cc lu lng lng/hi cao, m c hiu qu. ng nc ra cc hp cht aromatic v phn lc, cng nh qu trnh lm sch dung mi bng hp th, th ph hp vi qu trnh Tetra. d. Qu trnh Morphylex ca Krupp-Koppers Qu trnh ny c hot ng vi dung mi NFM c 4% nc. Qu trnh trch ly c thc hin trong thp c mm xuyn l kiu thng dng nhit cao khong 180oC. S chung ca qu trnh c hai im cng ngun gc so vi cc s trc. Mt ngun gc lin quan n thp stripping cc hp cht khng aromatic c bit nh l thp chng ct trch ly hon ton, ngha l bi s nhp dung mi tinh khit vo nh v do c mt khu vc ct v mt khu vc chng. u im ca s b tr ny l gii hn c s i ln ca cc hp cht aromatic trong phn ct distilat, mt mt iu ny cng gii hn lng nc c ha hi

55cng vi cc hp cht aromatic ny do ng ph, v mt khc gii hn s tun hon hydrocarbon v thp trch ly. Mt ngun gc khc nm ng nc ra cc hp cht hydrocarbon: nc i qua nh ca 2 thit b stripping c s dng cho ra phn lc, ri th nc c ni li vi dung mi c ti sinh n t y thp stripping cc hp cht aromatic nhm hydrate ha li dung mi trc khi tun hon v thp trch ly. 2.3.6. T l thu hi v tinh khit ca cc hp cht aromatic Tt c cc qu trnh trnh by u c th sn xut cc hp cht aromatic c cc ch tiu k thut v tinh khit nghim ngt nht, ty theo tnh hnh x l hon thin ti mt t nhm loi cc hp cht hydrocarbon cha bo ha l cc hp cht kh phn tch nht khi aromatic. Cc d liu cho theo v d trong Bng 7.28 i vi cc trng hp lm vic ca cc qu trnh Udex, Sulfolan, Arosolvan v DMSO, cho thy rng t l thu hi mi mt hp cht aromatic gn nh nhau i vi qu trnh ny so vi qu trnh khc. Ngc li, i vi tt c cc qu trnh, t l thu hi gim kh nhanh t benzen (>99,5%) n xylen (95-96%). T l ny tr nn nh (trung bnh 70%) i vi cc hp cht aromatic c 9 nguyn t C. 2.3.7. Cc d liu kinh t S so snh v kinh t chnh xc cc qu trnh l khng th thc hin c, do cc thng tin ban hnh khng bao gi c lin quan n cng mt trng hp c s. Chng ta v vy s gii hn trnh by trong Bng 7.29 cc d kin u t v tiu th m chng c th c ch trong vic nh gi kinh t s b mt d n. Cc d kin ny c lin quan vi c ng dng gii thiu trong Bng 7.28. Ch c mt hng dn ng ni m ta c th rt ra t y l: qu trnh Udex khng c tnh cnh tranh, nh chng ta nu. kt lun, qu trnh sn xut Benzen v toluen, hay sn xut Benzen, Toluen v Xylen t mt phn on C6-C7 hay phn on C6-C8 ca dng sn phm cracking hi hay ca dng sn phm reforming xc tc cn n cc qu trnh c tri qua chn chnh tt trong cng nghip, c kh nng cp cho cc hp cht aromatic cc ch tiu k thut nghim ngt nht cng vi hiu sut tt nht. Cc qu trnh ny c phn bit vi nhau do bn cht ca dung mi trch ly, chnh dung mi quyt nh n mt kha cnh khong thay i p dng v cc iu kin lm vic. Tuy nhin tht kh khn phn bit c chng trong ln phn tch th nht trn k hoch kinh t. S la chn mt qu trnh cho mt p dng c bit, v vy, phi c da trn s nghin cu su sc, c bit phi lu n tt c cc thng s a phng. 2.4. THIT B TRCH LY LNG LNG 2.4.1. Tng quan Nhm t c hiu qu cao, cu to thit b trch ly cn phi tha mn: Din tch tip xc ln nht gia cc pha (khu vc b mt tip xc), nhm lm cho cc qu trnh trao i pha d dng i vi mt dng hnh hc nht nh, cc iu kin vn hnh, c bit l nhit , c nh hng trc tip (thng qua cc h s phn b) hoc gin tip (t trng, nht...) n hiu qu trch ly. Vic la chn cng ngh v thit k cc cu trc bn trong cho mt h trch ly lng-lng c nh hng bi nhiu tiu chun nh sau: Lu lng tng (quyt nh n ng knh thp D) Cht lng sn phm (quyt nh n chiu cao thp H)

56 S khc nhau v t trng gia 2 pha (quyt nh n tc chuyn khi, H) T l cc pha (lng pha nh/lng pha nng, H) c trng ca s phn tn ( n nh, s to thnh nh tng bn..., quyt nh n s phn pha) S c mt ca cc cht rn (sn phm ca s phn hy, cn..., quyt nh n s phn pha) Cc iu kin vn hnh (nhit , p sut..., quyt nh n cu to thp) Khuynh hng ng cu (quyt nh n thi hn v sinh thp) Thi gian lu (quyt nh n nguy c phn hy cc sn phm) Tnh n mn (quyt nh n bn TB) Tnh bt chy ca mt trong cc sn phm (quyt nh n an ton) Din tch v chiu cao ca TB trch ly (quyt nh n mt bng phn xng) Cc quy ch c bit v vn hnh v an ton...

Hin tng trn ngc S trn ngc l mt hin tng din ra dc trc c khuynh hng ko di thi gian lu ca pha lin quan. Trong thc t, khi hin tng ny xy ra, mt phn pha lin quan c khuynh hng quay trn trong thit b trch ly, iu ny lm ko di thi gian lu ca pha trong khi mt phn khc ca pha s b bt buc phi vn chuyn nhanh hn, v tr ca phn pha ny b chim bi v tr ca phn pha b trn ngc. S trn ngc c hai hu qu tai hi n hiu nng ca thit b trch ly: Gim st hiu qu do s trn ngc mt phn ca mt hoc c hai pha Gim nng sut biu kin ca thit b trch ly, mt phn ca dng quay vng v do nhp liu mt cch v ch cho thit b Trong trng hp ca cc sn phm nhy cm, s gia tng thi gian lu ca mt phn sn phm c th gy nn s phn hy ca n. Cc nh ch to thit b thung ch trng vo s gim thiu hin tng trn ngc. (Hnh 7.34a) 2.4.2. H thng thit b trch ly Cc loi thit b trch ly c gp li thnh 2 nhm theo c ch tip xc pha c hay khng c tc ng ca nng lng c hc (khuy trn, a quay ...) trc tip ln hn hp cc pha ang tip xc vi nhau. Nhm khng c tc ng ca nng lng c hc gi l thit b trch ly loi tnh, nhm c tc ng ca nng lng c hc gi l thit b trch ly loi ng. Cc thit b trch ly loi tnh trong ng lc 2 pha tip xc vi nhau l nh chnh lch khi lng ring. Pha c lu lng nh phn tn vo trong lng pha lin tc. Thp ny c thun li l c nng sut ln song hiu qu chuyn khi li thp do b hin tng trn ngc mnh. Loi ny thng c dng khi qu trnh trch ly l n gin, dung mi d dng ko cu t cn tch ra khi pha lc. Nhm mc ch ci thin qu trnh phn tn ca cc pha (tc l tng hiu qu chuyn khi) bng cch hn ch ti a hin tng trn ngc, gia tng thi gian lu ca pha phn tn ng thi ci thin cht lng ca s phn tn, cc thit b trch ly c trang b thm cc kt cu bn trong nh cnh khuy, a quay hay cc c cu dao ng nhn nng lng c hc t bn ngoi, l cc thit b trch ly loi ng. 2.4.2.1. H thng thit b trch ly loi tnh a. My trn dng (Hnh 7.35)

57Cc my trn dng, cn gi l my trn tnh cho php khuy trn cc pha trong mt h thng ng dng. Dng c trn l do cu trc zic zac bn trong ch khng phi do nng lng bn ngoi tc ng. Chng c th c s dng nh cc my trn trong cc h thng trn lng. Chng cho php s phn tn kh tt, tn tht p sut nh v nh vy vn tc chy trong ng s rt u n, iu ny s lm gim thi gian lu. Cc thit b loi ny thng c ng dng trong cc qu trnh trch ly n gin. b. Thp phun to sng (Hnh 7.36) l mt h thng n gin nht, trong pha lin tc chy t do v c cho tip xc vi pha phn tn, pha ny i ngc dng qua pha lin tc. Cc h thng phun to sng n gin (khng c b phn ti phn phi pha phn tn) c dnh cho cc qu trnh trch ly d dng nht, v hiu qu chuyn khi ca chng nh. c. Thp so le (Hnh 7.37) Thp so le nhm ci thin hiu qu cc thp phun to sng. Cc tm so le dng a trn, k tip mt a hnh vnh khn hoc cc a hnh vin phn lp ngc nhau. S tip xc gia pha nng v pha nh c thc hin cho dng. Cc tm so le ny thc hin s khuy trn li ca pha phn tn.

Hiu qu ca mt h thng nh vy cng khng cao lm (0,05-0,2 bc l thuyt mt a thc t, gi tr ny cng ln ngha l hiu sut trch ly ca thp loi ny cng cao, ngha l m bo mt s bc trch ly nht nh, thp s khng cn cao, chi ph u t cho thp s nh), nhng chng c cc khu vc chuyn tip ln v cc cu trc a n gin l l do ng dng chng cho cc h thng c th ng cu v n mn.d. Thp mm c l (Hnh 7.38) Cc dng thp khng ngn hoc ngn n gin (a, b, c), trong cc dng pha chuyn ng lin tc t u ny n u kia thp, do vy hiu qu tip xc trn ln rt thp. Vi cc thp loi mm, sau mi ngn cc pha li tip xc li vi nhau, nh vy tng s lng cc giai on tip xc qua mi ngn: tip xc-lng phn pha-tip xc-lng phn pha nh vy, hiu qu trao i khi tng ln nhiu. Cc mm ca thp trch ly ny bo m c cc chc nng thu gp, ti trn sau ti phn tn pha phn tn. Hiu qu ca cc thp trch ly ny c ci thin r rng (khong 0,7 bc l thuyt mt mm) v cho d hin tng ng cu v n mn d xy ra, chng vn thng c u tin chn hn l cc thp loi thp so le. e. Thp m (Hnh 7.39)

Vt liu m ch c tc dng lm tng b mt tip xc ca 2 pha. Tt c cc loi m nh: m vng, yn nga, m cu trc u c th c s dng ty theo trng hp.Trong thi gian u, cc loi m yn nga (selle) bng cramique c s dng rng ri nhng hin nay chng khng cn c s dng na trong cc trng hp c bit cho d chng c u im chng n mn m tt nhng chng li c hn ch l: Tn tht p sut ln v nng sut gim (do h s trng nh, v m dy chim nhiu ch) Tnh d gy v khi sn xut (gy v khi c s gin n cc tng m) v khi lp t

58Cc m yn nga v m vng bng cramique c thay th bi cc m yn nga v m vng bng kim loi (IMPT ca Norton, vng Pall, CMR ca Glitsch, v.v.), chng d s dng hn, vng chc hn v cho php gim thiu kch thc thp.

Khuynh hng hin nay l s dng cc loi m cu trc nhm ci thin hn na hiu nng chuyn khi, tuy nhin vic s dng cng b hn ch do: Gi thnh kh ln C bn n mn yu hn (m cu trc c cu to mnh mai hn m yn nga v m vng) Kh khn trong vic tho lm v sinh.

m c kch thc cng nh (ng knh m nh) th hiu qu cng cao nhng nng sut cng gim v kh nng ng cu cng gia tng. Hiu sut chuyn khi ca thp m thng kh cao: bng 0,5-4 bc l thuyt/1m m.Thp m thng c s dng trong cc trng hp sau y: X l cc phn on du nhn bng furfural Tch loi H2S khi cc phn on du m Trch ly cc hp cht aromatic t cc phn on C6-C8 (qu trnh Duosol) Trch ly cc hp cht phnol t cc dng thi ca nh my lc du v ca qu trnh cc ha (qu trnh Phnosolvant) 2.4.2.2. H thng thit b trch ly loi ng a. Thit b trn-lng (Hnh 7.40) Trong cc h thng ny, giai on 1 l qu trnh khuch tn pha ny vo pha kia c thc hin nh nng lng bn ngoi (cnh khuy) trong 1 thit b trn, sau n giai on lng phn pha c thc hin trong 1 thit b lng ring. Hiu qu ca mi giai on ca thit b loi ny c th t n 90%. Cc thit b trn-lng c in m 2 giai on l tch bit nhau, s dng n gin nhng chim din tch mt bng ln. Chng c gp nhiu nht trong cc nh my c lu lng x l ln. Cc thit b l tch bit, d vn hnh cho tng qu trnh ring, nh vy vn tc khuy trn ln v vn tc lng cng ln v trong mi trng tnh. Mt dng thit b trn-lng c bit dng cho qu trnh trch ly cc hp cht aromatic, trong cc thit b trn-lng c chng cht ci ny ln ci khc trong cng mt thp (thp trch ly Mehner, Hnh 7.41). Cc thit b trn-lng c nh gi cao v hiu qu tng giai on cao v c linh ng cao (c th ng dng cho nhiu loi nguyn liu). Tuy nhin chng li c nhc im l gi c cao i vi cc h thng nhiu giai on v thng thng i hi phi c mt bng ln. b. Cc h thng quay

b.1. RDC v ARDC (Thit b tip xc a quay v thit b tip xc a quay khng i xng-Rotating Disc Contactor v Asymmetric Rotating Disc Contactor) Thit b RDC (Hnh 7.42) l 1 thp hnh tr trong c gn cc a c nh hnh vnh khn. Gia thp l 1 trc quay c gn cc a trn. Vng hot ng c to thnh khong gia a quay v a c nh. gn nh v y thp l cc vng lng (ni tho sn phm) c phn cch khi vng hot ng gia thp bi mt tm li nhm mc ch hn ch s khuy trong cc vng lng. Thit b ARDC (Hnh 7.43a) l mt s pht trin ca thit b RDC, trong trc c t lch tm nhm to 1 vng lng tng phn cho cc pha tng tng a. Phn

59 nh i vo trong RDC t vng pha di v i qua RDC ngc dng vi pha nng c a vo t vng pha trn. Mt trong cc pha c phn tn vo trong mi ngn nm gia hai vng c nh v kch thc ca cc git lng c iu khin bi vn tc quay ca a.Trong thit b RDC, ngoi tr cc vng ngoi ra, khng c s ni tip ca qu trnh phn tn v qu trnh kt dnh. S chuyn ng ca cht lng c to thnh t hai thnh phn, s quay v chuyn ng dc chm, c iu khin bi cc a quay v cc a vnh khn. Ngy nay, li c mt s thp RDC c s dng cc trng thi tnh khi RDC hot ng ging thp so le. l v cc l do ch yu sau: Cn gia tng cc i nng sut Tit kim nng lng trong sn xut Trong trng hp hiu qu trch ly ca thp RDC c nh l khng tha mn yu cu, ngi ta c th lp thm mt thp b sung, thng l thp m, hon tt cho thp RDC c nh hn l dng thp RDC quay. b.2. Cc thp trch ly quay khc (Hnh 7.43b, c, d) Cc loi thp trch ly khc c thit k nhm mc ch: t c hiu qu trch ly cao Gim thiu s trn ngc Ci thin s ti trn pha phn tn trong cc bc Cc thp trch ly quay c s dng trong rt nhiu ng dng quan trng: i vi thp RDC: trch ly cc hp cht aromatic (qu trnh Shell, Sulfolan) i vi thp Kuhni: trch ly cc hp cht aromatic (qu trnh IFP, DMSO) Cc thp trch ly khc nh thp Kuhni cng c s dng trong cng nghip ha cht, dc phm, x l nc thi, ... c. Cc thp trch ly lun phin Trong cc thp trch ly lun phin, s phn tn c bo m bi qu trnh khuy nh cc tc ng trc tip n khi lng ca cht lng v nh tc dng ca cc mm c l. Chng ta phn bit hai nhm thit b theo phn ng l: Cc thit b trong cc mm trng thi ng Cc thit b trong cc mm l c nh cn khi cht lng c khuy bi cc xung ng u n. c.1. Cc thit b c mm ng Thit b trch ly Karr (Hnh 7.44) c cu to bi mt dy cc mm c l (55-60% khu vc t do, l ng knh t 7-14mm) c mc vo nhau nh mt trc khuy chuyn ng dc lun phin. cc khong u n, c mt vng c gi vo nhm gim hin tng trn ngc. Nhm hng b c cu ny di ng dc v trnh s tip xc kim loi vi kim loi gia b c cu vi thp, cc vng bng PTFE (vt liu polyme) c ng knh ngoi ln hn so vi cc mm kim loi c t ngoi cng. Cc thp trch ly mm ng c s dng : Trch ly cc hp cht aromatic (qu trnh Union Carbide bng TEG) Trch ly cc hp cht phnol c trong nc thi nh my lc du (qu trnh Chempro)

60c.2. Cc thp xung Trong cc thp trch ly xung, cc cu trc bn trong c c nh cn khi cht lng c trong thp c khuy bi cc xung u n. Cu hnh ny c li im ln v n gim thiu c s lng cc chi tit c kh chuyn ng. Cc thp xung c phn bit vi nhau ch yu bi: B phn bn trong thp c th c to thnh t: cc mm tnh (mm c l chim ton b khu vc thp, hoc c cc a v vng Hnh 7.45.a) hoc m (Hnh 7.45.b) Phng cch to xung cho khi cht lng: c hc (v d bi mt ng thi chn thp Hnh 7.45.a) hoc kh ng (Hnh 7.45.b) Trong khi trong cc thp c mm tnh (tr thp xung) ch c mt pha chuyn qua cc l ca mm cn pha kia i qua cc ng chy chuyn, th trong cc thp xung c hai pha u chuyn lun phin qua cng cc l. iu ny bo m cho s phn tn ca mt trong cc pha v bo m s khuy, do bo m s ng th ha ca pha lin tc gia hai bc. Ngy nay cc thp xung ngy cng c s dng cho nhiu ng dng khc nhau nh x l dng thi, cng nghip dc phm... d. Cc thp trch ly ly tm Nhm d dng phn tch cc pha, mt vi nh thit k a ra cc thp trch ly c to ra mt trng trng lc nhn to c gia tc. Cc thit b ny c rt nhiu li im: Kh nng x l cc pha c t trng gn nhau Thi gian lu nh (p dng cho cc sn phm khng bn) Th tch thit b nh Chng t c s dng trong cng ngh du m do cc nhc im sau: Cc h thng c kh c vn tc ln ( tin cy, bo tr km) Gi cao Lu lng thp Kt lun Mt cch tng qut, vic chn la mt thit b trch ly chu nh hng ln bi kinh nghim tch lu c i vi mi ng dng. iu ny c bit r rng khi thit k mt cng on mi ca mt qu trnh c kim chng hoc khi thay th mt thit b ca mt cng on ang tn ti. Vic p dng ng mt qu trnh mi thng bt u t cc giai on th cc pilote (unit-pilote), trong phng th nghim sau mc bn cng nghip. Vic la chn cc thit b ny p dng mc cng nghip phi c tin hnh theo cc quy trnh nu trn v cc quy tc ngoi suy t cc thit b trch ly thng ng tin cy. Cc nh cng nghip v vy s c khuynh hng da vo nhng kinh nghim thu c t cc pilote v ch s gp rt t ri ro khi th mt kiu thit b trch ly mi cho mt cng on cng nghip.